1. Field of the Invention
The present invention relates to a power supply control system and to a semiconductor integrated circuit. For example, the present invention relates to a power supply control system and a semiconductor integrated circuit configured to enable power supply from a primary battery and a solar battery.
2. Description of the Related Art
Rapid development is recently occurring in technology for efficiently employing electricity obtained by converting natural energy into electrical energy employed as a drive source in electrical devices, in order to prevent deterioration of the planet's environment due to phenomena such as global warming. For example, use of solar batteries that converts sunlight directly into electrical energy is attracting attention. In some cases, solar batteries are connected to electrical devices and used on their own, and in some cases they are employed in combination with an existing battery (for example, a lithium primary battery).
A remote controller is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2011-61468. This remote controller employs a diode OR circuit to switch between a power supply circuit with a solar battery as the supply source, and a power supply circuit with another battery (a lithium primary battery) as the supply source, supplying power to a load by a combination of the solar battery and the other battery. A solar power generating system connected to a solar battery and another battery (a rechargeable battery) is disclosed In JP-A No. 9-261861. The solar power generating system reduces power loss due to voltage drop by making a forward direction current, flowing from the power source side towards the load, flow through a switching section with a smaller power loss than a reverse current prevention diode, when the voltage difference between the two ends of the reverse current prevention diode exceeds a specified value.
In the circuit illustrated in FIG. 9 of JP-A 2011-61468, a diode OR circuit configured by a pair of diodes is provided to prevent current from flowing into the solar battery and the lithium primary battery, respectively. In this circuit, when power is supplied from the solar battery or the lithium primary battery to the load which is a microcomputer, the power passes through one or the other of the diodes in the diode OR circuit. However, a voltage drop of at least the order of 0.7 V is incurred due to the electrical resistance of ordinary diodes, and a loss in the power supply to the load occurs. Such power loss is particularly evident in low power systems driven by a low voltage power sources.
The JP-A No. 9-261861 discloses a reverse current prevention device that prevents a reverse current from flowing from the rechargeable battery to the solar battery. Therefore, in a case in which a primary battery is connected to the reverse current prevention device disclosed in JP-A No. 9-261861, damage to the primary battery from a reverse current flowing into the primary battery may not be prevented.